Bright-background photos/renders and a tiny app icon were flagged as
AI-generated by the visible detectors. Two failure modes:
- Gemini sparkle on a bright background (snow+sky photo, white product
render) scored ~0.51. The FP gate only demoted on a low core-ring
brightness margin, which a bright background makes high. Add a gradient
floor (_SPARKLE_FP_GRAD 0.55): a real sparkle is a crisp star (grad
~0.97-1.0), a smooth luminance blob that NCC-matches the diamond is not
(the two FPs measured grad 0.105 / 0.463). The OR is a strict superset
of the old margin-only demotion, so it cannot regress dark/mid (kept by
margin) or white-bg (kept by confidence) real sparkles.
- A 48x48 geometric icon matched the Doubao/Jimeng CJK silhouette at
0.41/0.47 NCC. Purely a small-size artifact (the same icon at >=256px
collapses to ~0.06-0.10). Guard text-mark detection below a 200px short
side (_MIN_DETECT_SHORT_SIDE); real marks ship on full-resolution
renders (smallest captured sample 1086px).
Corpus re-sweep flips only OpenAI content and already-cleaned outputs,
all sub-0.5, so no provenance verdict changes. Add synthetic regression
fixtures for both modes; docs/module-internals.md updated.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Visible-watermark work across all three corner-mark engines plus a committed,
reproducible alpha-build pipeline (scripts/visible_alpha_solve.py) fed by committed
solid black/gray/white captures.
- jimeng: new "即梦AI" wordmark remover (reverse-alpha + thin residual inpaint,
always NCC-aligned -- the mark re-rasterizes/jitters per image). Detect via glyph
silhouette NCC (0.45 threshold; does not cross-fire with Doubao). Registered in the
visible-mark catalog; `visible --mark jimeng` / `--mark auto`.
- doubao: fix a real production defect -- the shipped remover left a READABLE
"豆包AI生成" outline on real samples while detect() returned conf 0.0 (fooled by a
thin outline), so the test passed and the "56/56 clean" claim was detector-measured,
not visual. Root cause: under-estimated alpha + fixed-geometry-no-inpaint + tight
locate box. Rebuilt alpha (careful gray-self solve), always-align, thin inpaint,
widened locate box -> readable outline becomes faint texture-level traces.
- gemini: rebuild gemini_bg_{96,48} from our own controlled captures (validated NCC
0.9998 vs the prior third-party asset); removal re-verified clean, no behaviour change.
- tests: add textured-shift regression to both engines (guards the align-on-shift path
the Doubao defect exposed; lesson: a detector-only removal test is insufficient,
assert visual residual).
- docs: CLAUDE.md, README, capture READMEs and docstrings synced; stale
"exact/pixel-exact/56-clean" claims removed.
Also includes a SynthID label-wording clarification in identify.py/cli.py
("SynthID pixel watermark" -> "SynthID watermark, inferred from C2PA metadata").
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Victor Kuznetsov